1. Field of the Invention
This invention relates to silicone water based elastomers reinforced with fumed silica filler.
2. Background Information
Aqueous silicone emulsions which yield elastomers when the water is removed are known. A silicone emulsion having a dispersed phase of an anionically stabilized hydroxylated polydiorganosiloxane and a colloidal silica and a continuous phase of water in which the pH is 9 to 11.5, which provides an elastomeric product upon removal of the water at ambient conditions is taught in U.S. Pat. No. 4,221,688, issued Sep. 9, 1980. The colloidal silica is added in the form of a dry powder or as an aqueous dispersion, preferably as a sodium ion stabilized aqueous dispersion of colloidal silica.
U.S. Pat. No. 4,427,811, issued Jan. 24, 1984, discloses a silicone elastomeric emulsion having improved shelf life. The method of manufacture mixes an anionically stabilized, hydroxyl endblocked polydiorganosiloxane, colloidal silica, and an alkyl tin salt, ages the mixture for at least two weeks, then adds the filler other than colloidal silica.
U.S. Pat. No. 4,584,341, issued Apr. 22, 1986, teaches a method of producing a latex of crosslinked polydiorganosiloxane which yields an elastomer upon removal of the water. The latex can be reinforced by adding greater than 1 part by weight of colloidal silica sol or silsesquioxane.
U.S. Pat. No. 4,634,733, issued Jan. 6, 1987, discloses a method of producing a silicone elastomer from an emulsion. The latex can be used immediately upon mixing of the ingredients. The composition includes colloidal silica.
U.S. Pat. No. 4,661,556, issued Apr. 28, 1987 teaches a method of producing a colloidal silica reinforced polydiorganosiloxane emulsion. The method combines an acidic aqueous colloidal silica sol and low molecular weight hydroxyl endblocked polydiorganosiloxane with anionic emulsifying agent, then homogenizes the mixture to form an emulsion. The emulsion is then mixed with surface active anionic catalyst and polymerized, then neutralized. A curable emulsion can be produced by mixing the reinforced polydiorganosiloxane emulsion with diorganotindicarboxylate and alkylorthosilicate.
U.S. Pat. No. 4,954,565, issued Sep. 4, 1990, teaches the use of tin (II) (stannous) catalyst in aqueous silicone emulsions of anionically stabilized, hydroxyl endblocked polydiorganosiloxane, silane crosslinker, and colloidal silica reinforcement.
Aqueous dispersions of pyrogenic silica are described in U.S. Pat. No. 2,984,629, issued May 16, 1961. A pyrogenic silica is worked until the apparent bulk density is increased to between about 6 and 15 lbs/cu.ft., mixed with water, and subjected to high shear in the presence of a sulfonic acid.